Without limiting the scope of the invention, its background is described in connection with implanting metals in silicon substrates. The diversity of nanometallic plasmonics and dielectric nanophotonics for trapping and shaping light is remarkable, but the integration of these discoveries with existing semiconductor processes is in doubt (Lindquist 2012, Brongersma 2010). Metamaterials, rationally designed materials to modify electronic properties, are a possible avenue to unite these divergent technologies (Kildishev 2013). For photovoltaics, the promise of nanoparticles at the surface or in the bulk, or nano-textured metal films on the back of the solar cell material to excite localized surface plasmon resonances (LSPR) which increase solar light trapping efficiency and decrease dimensions has been shown (Atwater 2010, Pillai 2010).
Voids are utilized to getter wide variety of metal impurities, which agglomerate in sensitive insulating regions of devices and adversely effect performance (Myers 2000). The formation of nanoparticles by direct ion implantation of a metal species, such as Au, and annealing has been investigated in Si which had cavities induced by hydrogen or silicon ion implantation and annealing (Wong-Leung 1995, Venezia 1998). Silver and platinum nanoparticles have been trapped in voids in silicon due to metal ion implantation and diffusion heat treatment (Kinomura 1998). It has been shown that crystalline damage caused by these multiple implantation methods can be eliminated for small amount of implanted metal, Au, Ag or Pt, only sufficient for monolayer coverage of voids (Wong-Leung 1996, Kinomura 2002). Multiple groups have also reported that Au monolayers on the inner surface of voids possess ordered structure (Wong-Leung 1996, Myers 1998). Cylindrical core/shell Ag/Si or Ag/SiO2 structures have been determined theoretically to have increased visible light absorption over pure Si, and voids with monolayer metal coverage may have similar plasmonic properties (Guillat 2010).
The yield of photoemission of small Ag particles, diameter 2 nm, is more than two orders of magnitude greater than that of bulk silver (SSS 1980). The combined effects of increased emission probability from a small particle and decrease in the photoelectric work function because of the small size lead to this large increase in photoelectric quantum yield (Chen and Bates 1986). Silver is the most suitable pure metal for plasmonics in the visible and NIR wavelength range because it has lowest electronic losses (West 2010).
Data on diffusion of Ag in Si is limited to high temperature (Rollert 1987), or only a few data points at temperatures deemed to be technologically important (Nason 1991, Chen 2002). High temperature study suggests that equilibrium concentration of Ag in Si is very low, 60× lower than that of Au, and is dominated by interstitial Ag that diffuses primarily by the dissociative mechanism (Rollert 1987). Substitutional Ag concentration is less than the measurement threshold at high temperature. Low temperature data, below the eutectic point of 830 C, shows that diffusivities obtained from high temperature cannot be extrapolated (Chen 2002, Nason 1991). Point defects in Si mediate Ag diffusion by the kick-out and dissociative mechanisms, involving vacancies and interstitial respectively, to increase the solubility above equilibrium. For monovalent group 11 metals Au and Cu in crystalline Si, chemisorption on the inner surface of a void decreases the Gibbs free energy more than formation of a silicide compound, whereas silicidation is more energetically favorable for multivalent Co and Fe (Petersen 1997).
Coincident site lattice heteroepitaxy of Ag on Si has 4:3 Ag:Si periodicity for (111) and (110) orientations, and 2:3 Ag:Si for (100) orientations. The different heteroepitaxial relationship for (100) is caused by smaller number of atomic planes in Ag fcc unit cell, three, compared to five in Si diamondlike unit cell. Heteroepitaxial Ag films on Si utilizing 4:3 and 2:3 coincident lattice have been observed (LeGoues 1988). Islands of Ag grown on H-terminated Si(111) are heteroepitaxial with Ag(110)//Si(110) strained −0.32% when Ag island diameter exceeds 12 nm, and Ag/Si (110) planes are misoriented up to 9° at smaller diameters (Li 2002).
Although films have been grown on surfaces for research and commercial purposes for a very long time as described above, growth on a created inner surface has not been demonstrated.